Sealed rolling bearings having seal assemblies for sealing the bearing space defined between the inner and outer races are typically used in an environment where there are large amounts of foreign matter including rolling oil, water and scales, such as for supporting iron-manufacturing pressure rolls used in rolling machines, in order to ensure high lubricity and sealability and prevent entry of foreign matter.
Such sealed rolling bearings are typically four-row tapered roller bearings comprising an inner race, an outer race, tapered rollers disposed between the inner and outer races, a retainer retaining the tapered rollers so as to be circumferentially spaced apart from each other, and seal assemblies.
The seal assemblies each comprise an annular seal case fitted on one end of the outer race, and a seal mounted in the seal case. The seal prevents leakage of lubricant in a bearing space, and also prevents entry of foreign matter such as rolling oil, water and scales into the bearing space from outside the bearing.
But according to the use environment of such sealed rolling bearings, especially if the bearing temperature changes, it was impossible to sufficiently prevent entry of foreign matter such as water from outside, for the following reasons.
When the air pressure in the bearing space rises above the atmospheric pressure (positive pressure is reached) due to a rise in bearing temperature, air leaks out through small gaps in the seal assemblies. When the bearing temperature drops thereafter and the air pressure in the bearing space drops below atmospheric pressure (negative pressure is reached), foreign matter such as water enters the bearing space together with air. Foreign matter tends to deteriorate lubricant and shorten the lifespan of the bearing.
To avoid this problem, sealed rolling bearings are proposed in which rollers are disposed in the bearing space defined between the inner and outer races, oil seals retained by seal holders are provided at the respective axial ends of the bearing space to seal the bearing space, and vent means are provided in the respective oil seals (see e.g. JP Patent Publication 11-062996A).
With the bearing disclosed in JP Patent Publication 11-062996A, when the air pressure in the bearing space drops below the atmospheric pressure, the bearing space communicates with the outside of the bearing through the vent means of the respective oil seals, thus reducing the air pressure in the bearing space to be close to the atmospheric pressure.
But the sealed rolling bearing disclosed in JP Patent Publication 11-062996A has a problem that when the bearing space is brought into communication with the outside of the bearing through the vent means, it is difficult to prevent passage of foreign matter such as water through the vent means, so that the foreign matter tends to enter the bearing space together with air. The vent means thus cannot sufficiently prevent entry of the foreign matter into the bearing space.
An object of the invention is to prevent generation of negative pressure in the bearing space and to prevent entry of foreign matter into the bearing.